1. Field of the Invention
The present invention relates to a method of fabricating a microlens and a structure thereof, and more particularly, to a method of fabricating a microlens with an etching process and a structure thereof.
2. Description of the Prior Art
CMOS image sensors (CISs) and charge-coupled devices (CCDs) are optical circuit components that represent light signals as digital signals. CISs and CCDs are used in the prior art. These two components widely applied to many devices, including: scanners, video cameras, and digital still cameras. CCDs use is limited in the market due to price and the volume considerations. As a result, CISs enjoy greater popularity in the market.
The CIS is manufactured utilizing the prior art semiconductor manufacturing process. This process helps to decrease the cost and the component size. It is applied in digital products such as personal computer cameras such as Web cams and digital cameras. Currently, the CIS can be classified into two types: line type and plane type. The line type CIS is applied in scanners, and the plane type CIS is applied in digital cameras.
Please refer to FIG. 1 to FIG. 2. FIG. 1 to FIG. 2 shows the CIS manufacturing process according to the prior art. As shown in FIG. 1, a semiconductor substrate 2 includes a plurality of shallow trench isolations (STI) 4 and a plurality of photodiodes 6. Each photodiode 6 connects electrically to at least one MOS transistor (not shown) such as reset transistor, current source follower, and row selector. The STI 4 is an insulator between these two adjacent photodiodes 6 for preventing the photodiode 6 from shorting with other components.
An inter layer dielectric (ILD) layer 8 is formed on the semiconductor substrate 2 to cover the photodiodes 6 and the STIs 4, and then a metallization process is performed on the ILD layer 8 to form a multilevel interconnects layer 9. The multilevel interconnects layer 9 includes an inter metal dielectric (IMD) layer 11 for isolation, and a metal layer 10 and a metal layer 12 serving as circuit connections of Metal-Oxide-Semiconductor (MOS) transistors. The metal layer 10 and the metal layer 12 are formed above every STI 4 for preventing each photodiode 6 from covering. The incident light (not shown) is gathered into the photodiode 6 without cross talk caused from the scattering. Next, a planarized layer 13 is formed on the metal layer 12, and the planarized layer 13 may be a multi-layer structure, for example, a silicon oxide layer formed by high density plasma process, or a plasma enhanced tetra-ethyl-ortho-silicate (PETEOS) layer formed by plasma enhanced chemical vapor deposition (PECVD) process with TEOS. Then, a passivation layer 14 such as a silicon nitride layer is formed for avoiding mist, and to prevent other impurities from entering the component area.
Thereafter, a color filter array (CFA) 18, which is combined by R/G/B filter patterns, is formed on the passivation layer 14. A spacer layer 20 is formed on the color filter array 18. A resin layer (not shown), which has the photoactive compound, is formed on the color filter array 18. In the prior art, the light source of the exposure process is a 365 nm wavelength UV (I-line). In the current technology, the micro-lens manufacture of the CIS most often uses I-line as the light source of the exposure process. After the 365 nm wavelength UV exposure and development, a light sensitization block 22 is formed to line up an array.
Please refer to FIG. 2. After the light sensitization block 22 is formed, a reflow process is performed. For example, the CIS 50 is exposed to high temperature for 5-10 minuets, and during the high temperature exposure, the resin material of the light sensitization block 22 changes, specifically, the shape of the resin layer is transformed by the high temperature of the reflow process. The light sensitization block 22 is a square in FIG. 1, and then, it becomes a microlens 24, which is almost a semicircular arc. After the reflow process, a passivation layer 26 is finally formed over the microlens 24, and the CIS 50 is finished.